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Forum / Schematic Design & PCB Layout / Redefine SD pins

Redefine SD pins

eugene128 , 12-02-2019, 10:19 PM

Hello. Is it possible programmatically reorder pins of SoM for connect SD-card ?

If it possible so how to do it better? Should I change *.dtsi ?

I've attached two images:

this is original connection in accordination with datasheet of TinyRex

this is what I want to do

Thanks!

robertferanec , 12-03-2019, 05:21 AM

This is very general question - at least you may need to say what chip you use.

PS: In some CPUs / Microcontrollers it may be possible to swap pins (if more pins has the same SD card function), but if you mean if you can just simple connect them in any order - I have never tried that, but I do not think that would work - I believe, SD card uses a specific protocol and it has some registers which would not be accessible if you swap pins.

Comments:

eugene128, 12-03-2019, 06:27 AM

Actually I want to attach this eMMC memory (https://www.mouser.com/datasheet/2/1...4G-1315796.pdf, 153FBGA p.8) to TinyRex (iMX6-TRM-43412331)

robertferanec , 12-04-2019, 12:02 AM

Have a look at iMX6 reference schematics, they have eMMC connected there. That could help.

Example from SABRESDB

Comments:

eugene128, 12-04-2019, 02:08 AM

Yes, that's it.But my main question: is it possible to "reorder logic" of PINs.for example now in accordination with datasheet of TinyxRex there is next connection:[SD/eMMC: PINX] --> [TinyxRex: CPU_GPIO2] --> [imx.6: SD4_DAT0]we want to reorder PINs and get next chain:[SD/eMMC: PINX] --> [TinyRex: CPU_GPIO2] --> [imx.6: SD4_DAT7]Now, as I understand right, TinyRex just provided that chain on "hardware" level.And if I want to be able to connect SD/eMMC with the own schematic without any modifications of SoM I should programmatically reorder imx.6's PINs logic so that SD4_DAT0 do logic of SD4_DAT7, and SD4_DAT7 do logic of SD4_DAT0.So, maybe that question for NXP.

robertferanec , 12-04-2019, 02:45 AM

Have a look into TinyRex schematic (you will get the module pdf schematic with development kit). You can find there where exactly the pins are connected and how you can swap them. For example, CPU_GPIO2 is connected to CPU pin D18 and as you can see you can not use it as SD4_DAT7 as it doesn't provide that as alternate function of D18 pin:

CPU SD4 mapping

J3 TinyRex baseboard pin mapping

J3 TinyRex module pin mapping